The principal purpose of point of purchase advertising display devices is to attract the attention of customers who are in the immediate vicinity so that they notice the name of the advertised product while having a favorable response to the appearance of the display device. At the same time, the device must be sufficiently inexpensive that a manufacturer or distributor of a product can buy the device in large quantities for use wherever his product is sold. For certain applications, such as the front of a vending machine, the device must be quite thin.
A common type of point of purchase advertising display device attracts attention by changing visual effects; and such changing visual effects may be produced in a number of different ways. A well known way to produce such changing visual effects is to use two cooperating sheets, one behind the other, with the forward sheet provided with a pattern that causes it to act as a shutter, exposing or concealing different parts of the rear sheet as the position of the front sheet changes relative to the line of sight from a viewer's eye to the rear sheet.
Devices of the foregoing general type are disclosed in Spiegel U.S. Pat. Nos. 829,492 and 911,561 (Re. 13,109); Morch U.S. Pat. No. 2,374,371; Newland U.S. Pat. No. 3,484,969; and Hasala U.S. Pat. No. 3,918,185. As shown by the two Spiegel patents, it is well known to produce the shift of the front sheet relative to a viewer's line of sight either by moving one of the two sheets or by fixing the two sheets a predetermined distance apart so that as a viewer moves relative to the display device his line of sight to the rear sheet is through different parts of the front sheet which therefore occupies different positions relative to the line of sight.
As shown by the above identified prior art, it is known to produce changing visual effects by providing a front sheet, or screen, which has parallel transparent and opaque strips, with a rear sheet, or screen, having contrasting strips that present one appearance if viewed from one angle and a different appearance if viewed from another angle. The present inventor has heretofore used this principle to produce a display device having brightly rear illuminated copy surrounded by a shifting field.
Morch U.S. Pat. No. 2,374,371 shows a way to utilize the techniques taught by the Spiegel patents to cause parts of a display to look as though they are moving.